In a high-stakes game of cat-and-mouse, overseas labs are churning out new synthetic drugs at a furious pace, often staying a step ahead of authorities and helping to fuel America’s rampant opioid crisis.

The United Nations Commission on Narcotic Drugs estimates that “new psychoactive substances”—a broad list that includes synthetic opioids—are emerging globally at an average rate of one a week. As with U-47700, rogue chemists sometimes piggyback on research by legitimate scientists that was abandoned before making it to the legal market.

Synthetic opioids are often more deadly than other kinds of common designer drugs, such as artificial cannabinoids or stimulants known as bath salts. Some opioids have flared up before—fentanyl variants caused problems on the West Coast in the late 1970s and 1980s—and they are roaring back at a perilous time.

The designer opioids mainly come from Chinese labs, the DEA says, and many labs sell them openly in online drug bazaars. On online forums, people compare notes on their experiences using the synthetics.

The U.S. surveillance system for these chemicals is a largely informal network of crime labs, medical examiners and law-enforcement authorities who share clues and alert each other when they find something new. It can be a laborious task, slowed in part by the challenge of finding something they didn’t know they were looking for.

At least six states specifically banned U-47700 before the DEA announced plans in September to make the drug illegal. DEA spokesman Rusty Payne said the agency’s scheduling actions are subject to “exhaustive reviews,” which take time.

So far this year through September, NMS Labs, a major private lab outside Philadelphia that works with states around the U.S., has tallied 105 overdose deaths related to U-47700 and 265 fatalities related to furanyl fentanyl—an analog, or chemical compound that is closely related to fentanyl. Axis Forensic Toxicology, a private lab firm in Indianapolis, has seen another 20 deaths linked to U-47700.

The U-47700-related fatalities span at least 31 states from Alaska to Utah to Florida.

The origins of U-47700 date to 1973, when Upjohn Co. asked its scientist Jacob Szmuszkovicz to create a drug with the pain-relieving power of morphine, but without the risk, according to a chapter he wrote for a 1999 book on drug research. Researchers wanted to find the Holy Grail that is elusive to this day: potent pain relievers that don’t have dangerous side effects, such as addiction and a potentially fatal slowdown in breathing.

By about 1974, Dr. Szmuszkovicz created a chemical Upjohn dubbed U-47700 at a company lab in Kalamazoo, Mich. Researchers knew it was a morphine-like drug when it triggered erect tails in mice, a reaction known as a Straub tail, says Phil von Voigtlander, a retired Upjohn research director who worked on the project.

Another test, which involved shining a hot light on mice’s tails to judge how long it took them to move, helped measure U-47700’s potency, says Dr. von Voigtlander. He learned the compound worked on the same receptor as morphine with roughly 7.5 times the strength.

Further rodent testing also revealed a downside. “Once we saw that it just caused tolerance and dependence like opioids and had opioid side effects, we thought, well, that’s just another morphine and that’s not what we’re looking for,” Dr. von Voigtlander says.

He calls U-47700 an important research steppingstone, and Upjohn patented the chemical. The company never tested U-47700 on people.

These kinds of pharmaceutical research efforts leave behind copious patents and scientific papers, which can serve as recipes for today’s enterprising chemists. Some researchers believe Chinese labs are scouring patent literature for new synthetic compounds to produce, before selling them.

Foreign labs began making U-47700 and offering it for sale online by late 2014, according to a forum on the social-media website Reddit devoted to discussion of chemical vendors and frequented by drug users. Buyers can choose from an array of online vendors selling synthetic drugs, including opioids, dubbed “research chemicals.”

The websites typically carry warnings that the chemicals they sell are “not for human consumption”—an attempt to gain legal cover, authorities say—and that buyers are responsible for complying with their home countries’ laws.

U-47700 began claiming lives in the U.S. by May 2015, when a 28-year-old man overdosed in Knox County, Tenn. The medical examiner there initially pegged his death to oxycodone, which was in his system. It took many more months to discover U-47700 was also there.

First, labs had to figure out what the drug was. NMS Labs detected U-47700 in November 2015 while testing blood samples from four different states at its facility outside Philadelphia.

“We actually found it by accident,” says Barry Logan, chief scientist there. U-47700 closely resembles a synthetic opioid called AH-7921—another research relic—which NMS had started watching for last year.

NMS, which is now rushing to create new tests to screen for 21 different designer opioids, eventually linked U-47700 to the Knox County case.

The NFL and NFL Players Association has added synthetic marijuana to the list of banned substances within its 2016 drug policy, according to a joint announcement by the league and union Wednesday.

Players and teams were informed in August of the change. The NFLPA made public the information Wednesday.

Per the policy, any player whose drug test reveals more than 2.5 ng/ML of synthetic cannabinoids will be in violation and subject to the normal course of intervention and potential discipline. It is one of nine drugs, including cocaine, PCP and traditional marijuana, that are part of the NFL's standard drug testing panel. The policy is developed jointly by the league and the NFL Players Association.

There are myriad dangers present when first responders, whether police or EMS, arrive at any emergency scene. Typically they are walking into unfamiliar territory.

With a recent influx of designer drugs, namely synthetic opioids, responders are now dealing with additional stress from more calls and a range of potencies in drugs.

Overdoses are becoming commonplace in Racine County and around the nation, according to Chris Eberlein, medical adviser for the southwest region of the Department of Health Services. And he sees increased wear on EMS personnel.

With so little information, it is difficult to determine the correct treatment to combat the effects of the illegal drugs. With drugs like Narcan, which is used to reverse the effects of opiate substances, the drug is usually harmless even if administered to a patient that had not taken an opiate substance.

A problem arises when responders have to administer drugs that may not react well with whatever the patient used. This has become more of an issue with the national influx of designer drugs. The chemical compounds are similar, but when mixed to create a drug cocktail, the effects increase.

Even with Narcan sometimes, there isn’t a guarantee drugs like it will have the same reactions.

“It’s important for responders to know that designer-drug users may not respond to naloxone in the same way a heroin user would respond,” said Barry Logan, chief of forensic toxicology at NMS Labs in Pennsylvania.

A dangerous strain of heroin with a “Game of Thrones”label has been circulating in Vermont and New Hampshire, where officials have counted nearly a dozen recent overdoses.

Vermont’s Department of Health said the strain of heroin is possibly laced with fentanyl, which makes the drug 50 times stronger. Fentanyl is a powerful opioid that is similar to morphine but is 50 to 100 times more potent, according to the National Institute on Drug Abuse. It’s usually used to treat severe pain.

The heroin bags being passed around bear the logo of the hit HBO show, which may be bolstering its popularity on the streets.

It was also involved in a 32-year-old man’s overdose in New Hampshire.

Although it was a fentanyl overdose that killed Prince April 21, the medical examiner said it was part of a deadly chemical cocktail.

A source close to the investigation says U47700 was part of the mixture. The potent painkiller is a synthetic opioid, eight times stronger than morphine.

Investigative sources told reporter Beth McDonough that Prince may have thought he was taking a legitimate painkiller, like hydrocodone or fentanyl, that unknowingly also had U-47700 in it.

The pills often look just like other medications. Plus, U47700 can be resistent to the life-saving antidote Narcan.

Because U-47700 is not considered a controlled substance by state or federal agents, it's not regulated. The Drug Enforcement Administrations says it tends to be produced overseas in China or Eastern Europe. It's widely available, easily accessible and affordable, about $40 online.

A new synthetic drug that can be purchased online and is connected to at least 50 deaths nationwide has several states scrambling to stop its spread, with Kansas law enforcement agencies seeking an emergency ban.

At least three other states — Ohio, Wyoming and Georgia — already have taken action to ban U-47700 after it was connected to overdoses. A spokeswoman for the U.S. Drug Enforcement Administration said that the agency is studying the opioid but hasn't yet moved to control it.

Nearly eight times more potent than morphine, U-47700 comes in various forms and can be injected, snorted or taken orally.

The U in the name stands for Upjohn, a pharmaceutical manufacturer that developed the drug in the mid-1970s as scientists were looking for a synthetic alternative to morphine, said Barry Logan, chief of forensic toxicology at NMS Labs in Willow Grove, Pennsylvania, which provides lab services for government and private clients.

"They were searching for a novel painkilling drug, the holy grail of analgesics that didn't have the addictive or respiratory depression properties of opiates or heroin," said Logan, who recently spoke about synthetic opioids at an international conference in Budapest.

The Upjohn researchers devised and patented several different compounds in search of their super drug, Logan said. Some of the compounds were written about in scientific literature, including methods for making them.

Chemists in China and Eastern Europe can find recipes for many of the drugs — including U-47700 — by combing through online patent records and old scientific journals, he said.

NMS has identified about 50 deaths across the U.S. that can be connected to U-47700, which came onto the company's radar screen in December, Logan said.

Legal synthetics have caused "upwards of 50 deaths" nationwide during the last four months, according to Barry Logan, director of the Center of Forensic Science and Education. The center is the nonprofit research arm of NMS Labs, which tests for the substances at its Willow Grove headquarters.

NMS confirmed one death in Illinois caused by W-18 and is investigating its role in another.

"The bigger problem right now is the designer opioid U-47700 and the designer fentanyl, furanyl, fentanyl," Logan said, adding that NMS had detected the two substances in a string of fatal overdoses that reached from Florida to Maine.

W-18 is a synthetic opioid considered to be 10,000 times more powerful than morphine and 100 time stronger than fentanyl—a street drug which caused about 270 overdose deaths last year in the province of Alberta alone.

Four kilograms of a white powder seized by police in the Edmonton area in December 2015 was analysed and turns out to be W-18, a drug that is not yet a controlled substance in Canada.

The quantity is enough to produce millions of tablets, say police. Minute amounts can be deadly. Police are concerned that illicit labs creating tablets may not cut the drug properly and that overdoses will result.

Hospitals have been warned to be on the lookout for drug overdoses and deaths that might be linked to W-18. Dr. Laura Calhoun of the government of Alberta health service joined with police to warn the public: “Our message to the public is this: no matter what drug you use, fentanyl or W-18 may be hiding in it, and they may kill you.”

There is new drug is on the streets of Northeast Ohio and it can be deadly.

In fact, an overdose death in Lake County is believed to be the first in the state, said Doug Rohde, supervisor of Chemistry and Toxicology at the Lake County Crime Laboratory.

After an alert from Lorain County about a new drug and some more research Rohde discovered it was U-47700. It is a new opioid that is eight times more potent than morphine. It is also deadly. U-47700 is to blame for the deaths of 20 people in 9 states.

The synthetic opioid is so new that it has not yet been labeled illegal. But, Rohde said just because it is still legal does not mean that it is safe.